Equilibration of siloxanes

ABSTRACT

The invention relates to a process for the preparation of equilibration products of organosiloxanes by rearrangement of the siloxane bond to a cation exchange resin, the organopolysiloxanes thus obtainable and the use thereof.

RELATED APPLICATIONS

This application claims priority to German application Serial No. 10 301355.5, filed Jan. 16, 2003, herein incorporated by reference.

BACKGROUND OF THE APPLICATION

1. Field of the Related Art

The invention relates to a process for the preparation of equilibrationproducts of organosiloxanes by rearrangement of the siloxane bond to acation exchange resin, the organopolysiloxanes thus obtainable and theuse thereof.

2. Description of the Invention

Equilibrations of siloxanes on ion exchange resins are part of the priorart. Among the multiplicity of known systems, the Amberlyst ionexchanger (in particular Amberlyst® 15) is a frequently used catalyticphase.

Thus, DE-A-21 52 270, which is hereby fully incorporated by referencewith regard to the present invention, describes a process for thepreparation of equilibration products of organosiloxanes byrearrangement of the siloxane bond on a cation exchange resin,organosiloxane used as starting material or an organosiloxane mixturebeing allowed to flow at a temperature of about 10° C. to about 100° C.through a packing which contains, as cation exchange resin, amacrocrosslinked cation exchange resin containing sulfo groups andhaving an average pore volume of at least about 0.01 cm³, and theorganosiloxanes which have flowed out being isolated.

In addition to the preparation of nonfunctional polydimethylsiloxanes,the possibility for the preparation of copolymericdimethylsiloxane/poly(methyl)hydrogensiloxanes by equilibration of amixture consisting of methylhydrogenpolysiloxane, hexamethyldisiloxaneand siloxane cycles on the macrocrosslinked ion exchange phaseAmberlyst® 15 is described therein.

Copolymeric dimethylsiloxane/poly(methyl)hydrogensiloxanes are, interalia, valuable starting materials in the preparation of PU stabilizers,in particular for hot flexible foam systems. On the basis of theteaching of DE-A-21 52 270, an attempt was made to prepare a provenstabilizer system by first bringing a mixture consisting ofhexamethyldisiloxane, poly(methyl)hydrogensiloxane and siloxane cyclesunder the action of Amberlyst® 15 as an acidic catalyst at 95° C. intoequilibration equilibrium, then subjecting it to a rearrangementreaction with a mixture of allylpolyethers with linkage of SiC bonds tothe siloxane backbones under the catalytic action of a platinum metalcomplex.

However, the polyethersiloxane obtained thereby was in the form of aturbid liquid whose stabilizing activity in the foaming of flexible foamsystems is limited in such a way that collapse results when they areused as a stabilizer.

OBJECT OF THE INVENTION

An object to be achieved consisted in finding a system which permits theequilibration of siloxanes carrying SiH groups, so that thesedisadvantages along the further processing route are avoided. These andother objects are apparent from the following Description of theInvention.

DESCRIPTION OF THE INVENTION

This invention provides for, inter alia, a process for the preparationof equilibration products of organosiloxanes by rearrangement of thesiloxane bond, said process comprising reacting at least twoorganosiloxanes in the presence of a macrocrosslinked cation exchangeresin containing sulfonic acid groups at a temperature of about 10° C.to about 120° C., optionally in the presence of a solvent, and isolatingthe equilibrated organosiloxanes, wherein said macrocrosslinked cationicexchange resin has a P value P≧2.2×10⁻³ m³/kg and A value≧35 m², where Pis the product of the specific surface area and the mean pore diameterof said macrocrosslinked resin and A is the specific surface area ofsaid macrocrosslinked exchange resin.

Surprisingly, it was found that, for example, Lewatit® K 2621, as an ionexchange resin having sulfonic acid groups, enable the equilibrationequilibrium to be established sufficiently rapidly and that thehydrogensiloxanes thus obtained are excellent starting materials for thepreparation of flexible polyurethane foam stabilizers.

This finding is surprising for a person of ordinary skill in the artsince this polymeric resin, as macroporous sulfonated polystyrene, has achemical parent structure which is identical to that of Amberlyst® 15and moreover also exhibits similar macroscopic properties, as shown inTable I: TABLE I Ion exchange Surface area Mean pore resin A (m²/g)diameter (nm) P (10⁻³m³/kg) Amberlyst ® 15 45 25 1,125 Lewatit ® K 262140 65 2,600

In the process in a preferred embodiment low molecular weight, inparticular linear organopolysiloxanes are depolymerized andequilibrated. In particular, an organosiloxane which is present in theequilibrium of the chemical compounds is isolated. In particular, anorganosiloxane whose viscosity is up to about 10 000 cP is used asstaring material. Especially preferred are organopolysiloxanes that arelow molecular weight organopolysiloxanes, such as those, for example,that contain from 3 to 200 silicon atoms.

In a further embodiment, a cation exchange resin whose mean porediameter is at least about 65 nm and whose average specific surface areais about 30 to 50 m²/g is used.

The rearrangement is preferably carried out at a temperature of about35° C. to about 100° C.

According to the invention, the process in a further embodiment iscarried out continuously; a fraction having the desired boiling range isseparated from the outflowing organosiloxane mixture, and the fractionhaving the undesired boiling range is recycled into the feed comprisingorganosiloxanes.

In particular, a mixture of hexamethyldisiloxane,poly(methyl)hydrogensiloxane and siloxane cycles is used as startingmaterial.

A further embodiment is the use of organosiloxanes for the linkage ofSiC bonds, a mixture of these organosiloxanes and allylpolyethers beingbrought into contact with a platinum metal complex and the polysiloxaneobtained being used as a flexible polyurethane foam stabilizer.

With the aid of the present invention, it is possible to preparestatistically uniformly composed organohydrogensiloxanes having adefined equilibrium of linear and cyclic compounds by equilibration of amixture of methylhydrogenpolysiloxane and cyclic or linear, optionallyhydrogen-functionalized polysiloxanes using a defined macrocrosslinkedcation exchange resin containing sulfonic acid groups. With regard tothese and-flier definitions, reference is made expressly to DE-A-21 52270.

It should be stated that all flexible foam stabilizers(polyethersiloxanes) which were prepared on the basis of Amberlyst® 15,Purolite® CT 169 D (surface area 35 to 50 m²/g, mean pore diameter 24.0to 42.5 nm) or Purolite® CT 165 (surface area 2.5 m²/g, mean porediameter>100) as an ion exchange system are turbid liquids which lead tocollapse of the PU foam. Important parameters for the description of thecatalyst phases to be used according to the invention are therefore thespecific surface area and the porosity, i.e. the mean pore diameter. Ifa product of the two variables is calculated it has the character of aninverse density (volume:mass) and permits a clear differentiationbetween the ion exchanger capable of functioning and ion exchangers notto be used according to the invention.

For the ion exchanger Lewatit® K 2621 used by way of example, theconsideration is as follows:40 m²/g×65 nm=2 600 m²nm/g=2.6×10⁻³m³/kg.

EXAMPLES

The advantage of the present invention is to be demonstrated on thebasis of the following non-limiting examples.

Working Examples

Preparation of the ion exchange resin containing sulfonic acid groupsand used in the example according to the invention and in the examplenot according to the invention

Lewatit® K-2621 in the commercial form having a high water content wasplaced in open evaporation dishes for a period of 18 hours in a dryingoven heated to 60° C. and then transferred in the still warm state inthe absence of moisture to vessels having an inert atmosphere and wasstored.

Amberlyst® 15 was used directly in the commercial form containing 5% ofwater.

Example 1 Preparation of a Hydrogensiloxane (Example According to theInvention)

A mixture consisting of 223.0 g of decamethylcyclopentasiloxane (D₅),20.2 g of poly(methyl)hydrogensiloxane PTF1 (SiH content: 15.75 eq/kg)and 6.9 g of hexamethyldisiloxane HMDS (61.5 mol of D₅:0.135 mol ofPTF1:0.865 mol of HMDS), was mixed with 3 mol % of predried ion exchangeresin, Lewatit® K-2621 and equilibrated for 6 hours at 95° C. withcontinuous stirring and, after cooling of the reaction mixture, the ionexchange resin was separated by filtration. The content of active SiHwas determined with the aid of gas volumetry (decomposition of a weighedsiloxane sample with the aid of a sodium butylate solution) as 1.26eq/kg. The viscosity of the hydrogensiloxane was 86.4 mPa·s (25° C.).

²⁹Si-NMR spectroscopy assigned to the hydrogensiloxane obtainedaccording to the invention an average structure which could berepresented by the following formula:(CH₃)SiO—[(CH₃)₂SiO—]_(61,5)[CH₃)HSiO—]_(6,5)Si(CH₃)₃

Comparative Example 1 Preparation of a Hydrogen Siloxane

A mixture consisting of 223.0 g of decamethylcyclopentasiloxane (D₅),20.2 g of poly(methyl)hydrogensiloxane PTF1 (SiH content: 15.75 eq/kg)and 6.9 g of hexamethyldisiloxane HMDS (61.5 mol of D₅:0.135 mol ofPTF1:0.865 mol of HMDS) was mixed with 3 mol % of ion exchange resinAmberlyst® 15 and equilibrated for 6 hours at 95° C. with continuousstirring and, after cooling of the reaction mixture, the ion exchangeresin was separated by filtration. The content of active SiH wasdetermined with the aid of gas volumetry as 1.26 eq/kg. The viscosity ofthe hydrogensiloxane was 80.3 mPa·s (25° C.).

²⁹Si-NMR spectroscopy assigned to the hydrogensiloxane obtained in thismanner the following average structure:(CH₃)SiO—[(CH₃)₂SiO—]_(61,5)[CH₃)HSiO—]_(6,5)Si(CH₃)₃

Example 2 Further Processing of the Hydrogensiloxane Obtained in Example1 to Give a Polysiloxane/Polyoxyalkylene Block Copolymer

259.2 g (0.185 mol) of a polyether of the average formulaCH═H—CH₂O—(C₂H₄O—)₅(C₃H₆O—)₂₁CH₃,

86.4 g (0.062 mol) of a polyether of the average formulaCH₂═H—CH₂O—(C₂H₄O—)₂₆(C₃H₄O—)₄CH₃,

234.5 g (0.061 mol) of a polyether of the average formulaCH═CH—CH₂O—(C₂H₄O—)₄₅(C₃H₄O—)₃₄CH₃,

156.4 g (0.041 mol) of a polyether of the average formulaCH₂═CH—CH₂O—C₂H₄O—)₃₆(C₃H₄O—)₃₈H and

37.0 g (0.061 mol) of a polyether of the average formulaCH₂H—CH₂O—C₂H₄O—)₁₄CH₃were initially introduced together with 15.4 mg of cis-(NH₃)₂PtCl₂ intoa flask provided with a dropping funnel, stirrer, thermometer, gas inletand reflux condenser. The apparatus was blanketed by means of a gentlenitrogen stream. After heating to 120° C., 240 g (=0.301 mol of SiH) ofthe hydrogensiloxane from example 1 was added dropwise in the course of30 minutes. The reaction mixture was allowed to continue reacting for 3hours, and a quantitative SiH conversion (determined by gas volumetry byreaction with sodium butylate solution) was achieved. After filtrationover a Seitz-K-300 filter disk, a clear, slightly yellowish product wasobtained.

Comparative Example 2 Further Processing of the HydrogensiloxaneObtained in Comparative Example 1 to Give a Polysiloxane(Polyoxyalkylene Block Copolymer)

Analogously to example 2, 259.2 g (0.185 mol) of a polyether of theaverage formulaCH₂═CH—CH₂O—(C₂H₄O)₅(C₃H₆O—)₂₁CH₃,

86.4 g (0.062 mol) of a polyether of the average formulaCH₂═H—CH₂O—(C₂H₄O—)₂₆(C₃H₆O—)₄CH₃,

234.5 g (0.061 mol) of a polyether of the average formulaCH₂═CH—CH₂O—(C₂H₄O)₄₅(C₃H₆O—)₃₄CH₃,

156.4 g (0.041 mol) of a polyether of the average formulaCH═H—CH₂O—(C₂H₄O—)₃₆(C₃H₆O—)₃₈H and

37.0 g (0.061 mol) of a polyether of the average formulaCH₂═CH—CH₂O—(C₂H₄O—)₁₄CH₃

were initially introduced together with 15.4 mg of cis-(NH₃)₂PtCl₂ intoa flask provided with a dropping funnel, stirrer, thermometer, gas inletan reflux condenser. The apparatus was blanketed by a gentle nitrogenstream. After heating to 120° C., 240 g (=0.301 mol of SiH) of thehydrogensiloxane not according to the invention and from comparativeexample 1 were added dropwise in the course of 30 minutes. The reactionmixture was allowed to continue reacting for 3 hours, a quantitative SiHconversion (determined by gas volumetry by reaction with sodium butylatesolution) was achieved. In spite of the quantitative SiH conversion, thepolysiloxane/polyether copolymer obtained was a turbid opaque, slightlyyellowish liquid which did not become clear even after filtration over aSeitz-K-300 filter disk.

Example 3 Comparative Example 3

The testing of the performance characteristics of the foam stabilizersprepared was carried out using a foam formulation in the followingmanner:

In each case 300 parts of a commercial polyether for the preparation offlexible polyurethane foams, which had three hydroxyl groups in theaverage molecule and had a molecular weight of 3 500, were mixed with 15parts of water, 15 parts of a physical blowing agent, the correspondingamount of foam stabilizer to be tested, according to example 2 accordingto the invention or comparative example 2, 0.33 part ofdiethylenetriamine and 0.69 part of tin octanoate, with thoroughstirring. After addition of 189 parts of toluene diisocyanate (isomermixture of 2,4 and 2,6 in the ratio of 4:1), stirring was effected for 7seconds at 2 500 rpm using a Glatt stirrer, and the mixture was pouredinto a box opens at the top. A fine-pored foam which, was characterizedby the following parameters formed:

1. The sag of the foam at the end of the rise phase (denoted by “Sag” intable II).

2. The number of cells per centimeter of foam, which was determined bymicroscopy.

Table II compares the measured values for 2 different concentrations(1.8 parts/1.5 parts) of the stabilizer obtained by the processaccording to the invention (example 2) and of the stabilizer notprepared according to the invention (product of comparative example 2).TABLE II Example Sag Cells per centimeter Example 3 0.7/1.4 15Comparative example 3 collapse n.d.

The above description is intended to be illustrative and not limiting.Various changes or modifications in the embodiments described herein mayoccur to those skilled in the art. These can be made without departingfrom the scope and spirit of the invention.

1. A process for the preparation of equilibration products oforganosiloxanes by rearrangement of the siloxane bond, said processcomprising reacting at least two organosiloxanes in the presence of amacrocrosslinked cation exchange resin containing sulfonic acid groupsat temperature of about 10° C. to about 120° C., optionally in thepresence of a solvent, and isolating the equilibrated organosiloxanes,wherein the said macrocrosslinked cation exchange resin has a Pvalue≧2.2×10⁻³ m³/kg and A value≧35 m² wherein P is the product of thespecific surface area and the mean pore diameter of saidmacrocrosslinked resin and A is the specific surface area of saidmacrocrosslinked exchange resin.
 2. The process as claimed in claim 1,wherein the at least one of the organosiloxanes has at least one Si—Hgroup.
 3. The process as claimed in claim 1, wherein the organosiloxanesare low molecular weight organopolysiloxanes.
 4. The process as claimedin claim 1, wherein the low molecular weight organopolysiloxanes havebetween 2 and 200 silicon atoms.
 5. The process as claimed in claim 1,wherein the solvent is an aliphatic hydrocarbon.
 6. The process asclaimed in claim 1, wherein the isolated equilibrated organosiloxane isan organopolysiloxane.
 7. The process as claimed in claim 1, wherein themean pore diameter of the macrocrosslinked cation exchange resin is atleast about 65 nm.
 8. The process as claimed in claim 1, wherein thetemperature is about 35 to about 100° C.
 9. The process as claimed inclaim 1, wherein the organosiloxanes have viscosity of up to about10,000 cP.
 10. The process as claimed in claim 1, wherein themacrocrosslinked cation exchange resin has specific surface area about30 to 50 m²/g.
 11. The process as claimed in claim 1, wherein theprocess carried out continuously.
 12. The process according to claim 11,wherein the equilibrated organosiloxanes are isolated by fractionaldistillation and the fraction having the desired boiling range isseparated from the fraction(s) having equilibrated organopolysiloxaneshaving the undesired boiling range(s) and removed and the fraction(s)having the undesired boiling range(s) are recycled back into the feed ofthe continuous process.
 13. The process as claimed in claim 1, whereinat least one of the organosiloxanes is hexamethyldisiloxane,poly(methyl)hydrogensiloxane or a cyclic siloxane.
 14. An equilibratedorganopolysiloxane obtainable by the process as claimed in claim
 1. 15.The process according to claim 1 wherein the equilibratedorganosiloxanes are further reacted with at least one allylpolyethylenein the presence of a platinum metal complex.
 16. A method forstabilizing a flexible polyurethane foam which comprises adding theorganopolysiloxane foam to a mixture comprising a polyetherpolyol and anisocyanate.